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Internet Engineering Task Force (IETF) J. Mauch
Request for Comments: 8212 Akamai
Updates: 4271 J. Snijders
Category: Standards Track NTT
ISSN: 2070-1721 G. Hankins
Nokia
July 2017
Default External BGP (EBGP) Route Propagation Behavior without Policies
Abstract
This document updates RFC 4271 by defining the default behavior of a
BGP speaker when there is no Import or Export Policy associated with
an External BGP session.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8212.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Changes to RFC 4271 . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Transition Considerations for BGP Implementers . . . 6
A.1. "N+1 N+2" Release Strategy . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 6
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
BGP routing security issues need to be addressed in order to make the
Internet more stable. Route leaks [RFC7908] are part of the problem,
but software defects or operator misconfiguration can also
contribute. This document updates [RFC4271] so that routes are
neither imported nor exported unless specifically enabled by
configuration. This change reduces the consequences of these
problems and improves the default level of Internet routing security.
Many deployed BGP speakers send and accept any and all route
announcements between their BGP neighbors by default. This practice
dates back to the early days of the Internet, where operators were
permissive in sending routing information to allow all networks to
reach each other. As the Internet has become more densely
interconnected, the risk of a misbehaving BGP speaker poses
significant risks to Internet routing.
This specification intends to improve this situation by requiring the
explicit configuration of both BGP Import and Export Policies for any
External BGP (EBGP) session such as customers, peers, or
confederation boundaries for all enabled address families. Through
codification of the aforementioned requirement, operators will
benefit from consistent behavior across different BGP
implementations.
BGP speakers following this specification do not use or send routes
on EBGP sessions, unless specifically configured to do so.
2. Terminology
[RFC4271] describes a Policy Information Base (PIB) that contains
local policies that can be applied to the information in the Routing
Information Base (RIB). This document distinguishes the type of a
policy based on its application.
Import Policy: a local policy to be applied to the information
contained in the Adj-RIBs-In. As described in Section 3.2 [RFC4271],
the Adj-RIBs-In contain information learned from other BGP speakers,
and the application of the Import Policy results in the routes that
will be considered in the Decision Process by the local BGP speaker.
Export Policy: a local policy to be applied in selecting the
information contained in the Adj-RIBs-Out. As described in
Section 3.2 [RFC4271], the Adj-RIBs-Out contain information that has
been selected for advertisement to other BGP speakers.
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Changes to RFC 4271
This section updates [RFC4271] to specify the default behavior of a
BGP speaker when there are no Import or Export Policies associated
with a particular EBGP session. A BGP speaker MAY provide a
configuration option to deviate from the following updated behaviors.
The following paragraph is added to Section 9.1 (Decision Process)
after the fifth paragraph, which ends in "route aggregation and route
information reduction":
Routes contained in an Adj-RIB-In associated with an EBGP peer
SHALL NOT be considered eligible in the Decision Process if no
explicit Import Policy has been applied.
The following paragraph is added to Section 9.1.3 (Phase 3: Route
Dissemination) after the third paragraph, which ends in "by means of
an UPDATE message (see 9.2).":
Routes SHALL NOT be added to an Adj-RIB-Out associated with an
EBGP peer if no explicit Export Policy has been applied.
4. Security Considerations
Permissive default routing policies can result in inadvertent effects
such as route leaks [RFC7908], in general resulting in routing of
traffic through an unexpected path. While it is possible for an
operator to use monitoring to detect unexpected flows, there is no
general framework that can be applied. These policies also have the
potential to expose software defects or misconfiguration that could
have unforeseen technical and business impacting effects.
The update to [RFC4271] specified in this document is intended to
eliminate those inadvertent effects. Operators must explicitly
configure Import and Export Policies to achieve their expected goals.
There is of course no protection against a malicious or incorrect
explicit configuration.
The security considerations described in [RFC4271] and the
vulnerability analysis discussed in [RFC4272] also apply to this
document.
5. IANA Considerations
This document does not require any IANA actions.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <http://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>.
[RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
and B. Dickson, "Problem Definition and Classification of
BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June
2016, <http://www.rfc-editor.org/info/rfc7908>.
Appendix A. Transition Considerations for BGP Implementers
This appendix is not normative.
For an implementer, transitioning to a compliant BGP implementation
may require a process that can take several years.
It is understood and acknowledged that operators who are taking
advantage of an undefined behavior will always be surprised by
changes to said behavior.
A.1. "N+1 N+2" Release Strategy
An implementer could leverage an approach described as the "N+1 and
N+2" release strategy. In release N+1, the implementer introduces a
new default configuration parameter to indicate that the BGP speaker
is operating in "ebgp insecure-mode". In addition to the
introduction of the new parameter, an implementer could begin to
display informational warnings to the operator that certain parts of
the configuration are incomplete. In release N+1, operators of the
BGP implementation become aware that a configurable default exists in
the implementation, and can prepare accordingly. In release N+2 or
later, the inverse of the previous default configuration parameter
that was introduced in release N+1 becomes the new default.
As a result, any new installation of release N+2 will adhere to this
document. Installations upgraded from version release N+1 will
adhere to the previous insecure behavior, if no modification was made
to the "ebgp insecure-mode" configuration parameter.
Acknowledgments
The authors would like to thank the following people for their
comments, support and review: Shane Amante, Christopher Morrow,
Robert Raszuk, Greg Skinner, Adam Chappell, Sriram Kotikalapudi,
Brian Dickson, Jeffrey Haas, John Heasley, Ignas Bagdonas, Donald
Smith, Alvaro Retana, John Scudder, and Dale Worley.
Contributors
The following people contributed to successful deployment of the
solution described in this document:
Jakob Heitz
Cisco
Email: jheitz@cisco.com
Ondrej Filip
CZ.NIC
Email: ondrej.filip@nic.cz
Authors' Addresses
Jared Mauch
Akamai Technologies
8285 Reese Lane
Ann Arbor Michigan 48103
United States of America
Email: jared@akamai.com
Job Snijders
NTT Communications
Theodorus Majofskistraat 100
Amsterdam 1065 SZ
The Netherlands
Email: job@ntt.net
Greg Hankins
Nokia
777 E. Middlefield Road
Mountain View, CA 94043
United States of America
Email: greg.hankins@nokia.com

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